Organbuilder,
The headlights are powered by the battery. The battery supplies voltage, say 12 volts, and also has the capability to deliver a HUGE amount of current. This huge reserve of power in the battery is just sitting there waiting for something to use it. The starter uses lots of current, the headlights use a little current, the coil uses only a tiny bit of current. These things only use what they were designed to use. Although this huge reserve is there waiting, the coil would never use the current that the starter would use even though it hooked to the same battery. Voltage is present in the wires all the time but nothing flows until the headlight is turned on and 'asks' for current.
The trickle charger must produce enough voltage to overcome the battery, but the 'trickle' part isn't voltage, it's a trickle of current.
Stuart
